The sonobuoy originated from military submarine detection¡Ait was also used to measure ocean acoustic signal by scientists¡Abut the continuous recording and transmitting design by early sonobuoy is not suitable for long-term or scheduled observations. In this research¡A¡§off the self¡¨ components were integrated to develop an autonomous sonobuoy¡Awhich can be used to measure shipping noise and marine life acoustic signal in coastal water. The electronic design is based on a PC motherboard¡Ait is currently configured with a maximum sampling rate of 44.1 kHz¡Aand a maximum storage capacity of 40 GB. The sound was collected by a plug and play hydrophone system¡Awhich is controlled by a program written by LabVIEW. In addition to the programmable data acquisition and low cost advantages¡Athe flexible design allows quick system expansion and adjustment¡Ait can also be configured to record from multiple transducers.

Thesis (Ph.D.)--Drexel University, 2010. / Includes abstract and vita. Includes bibliographical references (leaves 158-163).

A design for a deep ocean hydrophone is proposed here. The hydrophone's sound sensing element is comprised of a capped end, piezoelectric cylinder. This sound sensing element is encased in an acoustic coupling fluid filled elastomeric boot. A small diameter tube communicates hydrostatic pressure from the coupling fluid to the interior of the sound sensing element for hydrostatic pressure compensation. The theoretical free field voltage sensitivity, the ratio of open circuit voltage to incident acoustic pressure, is predicted from mathematical model of the sound sensing element.

Approved for public release; distribution is unlimited / A simple low-noise hydrophone design with internal preamplifier is presented. This design is similar to published designs and is a variation of the design developed in the NPS thesis by Miguel Alvarado [2003], except that several improvement features are included. These include a simplification of the structure and its modes of vibration, a large reduction in package diameter and the effect its acoustic diffraction has on the sensitivity, and an extended upper frequency response of 42 kHz resulting from the simplified structure and reduced diameter. Furthermore, the modified geometry along with its orientation in the water should produce a very omni-directional response in the horizontal plane at the higher frequencies. Finally, an new feedback preamplifier design developed by Hofler and Alvarado was discovered to have some subtle but serious performance problems. These problems were resolved in this research and the resulting preamplifier performance was tested and documented herein. / Lieutenant, Hellenic Navy

Because the acoustic wave is capable of propagating at a long-distance in water, the hydrophone plays a key role in the underwater acoustic sensing all the time. The hydrophone based on fiber optic interferometry has an extremely high sensitivity and large dynamic range. In addition, the electrically passive, immunity to electromagnetic interference, and multiplexing properties of fiber optic sensor offer great advantages over traditional piezoelectric hydrophone. Due to the complete path-balance between the two counterpropagating waves, a Sagnac interferometric configuration can employ a low-coherent light source to reduce the cost. This configuration can easily route optical paths and replace sensor heads to compare with each other. But, the sensitivity varying with frequency and the polarization-induced signal fading problem make it unsuitable for applications in need of detecting correct amplitude of signals. The Michelson interferometric configuration with Farady rotator mirror (FRM) has a constant sensitivity and solves the polarization-induced signal fading problem. But, this configuration uses a high-coherent light source and expensive FRMs, and be difficult to route. In this paper, we use the polarization-insensitive Michelson fiber optic sensor to adjust the demodulation circuits we design. In this paper, we establish the interferometric hydrophones. The fiber optic coil of the sensor head is embedded with the special materials in order to acoustic impedance matching and waterproofing. We employ phase generated carrier demodulation technology to get the acoustic signal of interest from the output of the interferometer. In our experiment, the dual Sagnac configuration has a dynamic range of 23 dB and a sensitivity of -226 dB re V/1uPa, the Michelson configuration with FRMs has a dynamic range of 25 dB and a sensitivity of -204 dB re V/1uPa.

Thesis (M.S. in Physical Oceanography and Meteorology)--Naval Postgraduate School, Dec. 2004. / Thesis Advisor(s): Ching-Sang Chiu. Includes bibliographical references (p. 33). Also available online.

Three different optical fiber phase modulators utilizing the magnetostrictive properties of the metallic glass alloy Fe74Co10B16 were constructed. By binding the optical fiber to the magnetostrictive metallic glass, the strain imparted to the metallic glass from the magnetic field is transferred to the optical fiber. The strain on the optical fiber shifts the phase of the light, which can be controlled indirectly by varying the current producing the magnetic field permeating the metallic glass. The performance of the modulators on the basis of optical phase shift as a function of bias magnetic field and optical phase shift as a function of excitation frequency was measured. Speculations were made on the loss mechanism inherent in the various modulator designs in order to explain the deviation in performance of the three modulator designs.

Dual purpose fiber optic microbend loss sensors have been developed for measurement of underwater acoustic wave amplitudes and for detection of the direction of wave propagation. Cylindrical sensing elements with external threads have fibers wound around them. Axial slots, cut along the length of the cylinder and deeper than the threads, provide the microbends. Three different construction schemes for cylindrical sensing elements are built. The dual purpose hydrophones are characterized for frequencies ranging from 15 kHz to 75 kHz. Based on the results, an improved design that uses the wavelength dependence of microbend loss in a single mode fiber is proposed. / Master of Science

Les ultrasons de puissance, pierre angulaire de la sonochimie, constituent un domaine récurrent de la recherche en génie des procédés. Leurs effets mécaniques et chimiques permettent l’intensification de processus physiques (mélange, dissolution, émulsion, dégazage, attrition …) et l’activation de réactions (via la production de radicaux libres). Le phénomène sous-jacent est la cavitation acoustique inertielle (ou transitoire), qui correspond à l’implosion violente de bullescréées lors des phases de dépression de l’onde, conduisant localement à des conditions extrêmes de température et pression, et à la formation de micro-jets puissants vers les surfaces solides. Malgré ce fort potentiel, les applications industrielles des ultrasons de puissance sont rares. Ceci s’explique principalement par le fait que la cavitation transitoire est encore mal comprise et maîtrisée empêchant la conception de réacteurs sonochimiques efficaces à l’échelle pilote. Le verrou principal réside dans la prédiction et l’optimisation de la localisation des zones sonoactives. En effet, les ultrasons de puissance sont atténués de façon significative sur de courtes distances, en particulier dans les milieux polyphasiques, fréquemment rencontrés dans les procédés physico-chimiques. Dans ce contexte, cette thèse s’intéresse à évaluer localement les effets physiques des ultrasons (20 kHz) appliqués à une suspension liquide-solide. Il s'agit d’identifier les zones d’activité des ultrasons dans un réacteur à lit fluidisé et à sonde plongeante et de préciser l’influence de différents paramètres opératoires (puissance émise, vitesse du fluide, concentration et propriétés de la suspension). La première partie évalue l’atténuation de l’onde ultrasonore liée à la cavitation et la présence de solide, ainsi que l’évolution de son spectre de fréquences. En effet, les bulles de cavitation présentent une signature acoustique propre. Dans cet objectif, des mesures de pression acoustique sont réalisées axialement à l’aide d’un hydrophone piézoélectrique et interprétées par analyse spectrale. Le second volet quantifie les effets physiques des ultrasons via une mesure locale du coefficient de transfert liquide-solide par méthode électrochimique. Les cartographies du réacteur réalisées à l’aide de microélectrodes permettent d’identifier les zones d’intensification marquée. Mises en regard avec les mesures précédentes, elles font le lien entre l’accélération du transfert de matière local et les caractéristiques du signal acoustique mesuré à proximité. Enfin, l’étude expérimentale est complétée par des simulations numériques du réacteur réalisées avec COMSOL Multiphysics. Le modèle prend en compte la dissipation de l’énergie par les bulles, qui joue un rôle majeur dans l’atténuation des ultrasons. Via une étude paramétrique, ces simulations montrent aussi le rôle du design du réacteur sonochimique sur la localisation des zones actives. / Power ultrasound, the cornerstone of sonochemistry, is a recurring research area in process engineering. Their mechanical and chemical effects allow the enhancement of physical processes (mixing, dissolution, emulsion, degassing, attrition …) and the activation of chemical reactions (via free radicals production). The underlying phenomenon is the inertial (or transient) acoustic cavitation, which stands for the violent collapse of bubbles generated during the depression phases of the wave, leading locally to extreme conditions of pressure and temperature and to the formation of powerful micro-jets pointing towards solid surfaces. Despite this high potential, industrial applications of power ultrasound are scarce. This is mainly due to the fact that transient cavitation is still poorly understood and controlled, preventing the design of efficient sono-reactors on a pilot scale. The main obstacle lies in the prediction and optimization of the spatial distribution of sono-active zones. Indeed, power ultrasound is markedly attenuated over short distances, particularly in multiphase media, frequently encountered in physicochemical processes. In this context, this thesis aims at evaluating locally the physical effects of power ultrasound (at 20 kHz) applied to a liquid-solid suspension. The sono-active zones of a fluidized bed reactor equipped with an ultrasonic horn are identified and the influence of various experimental parameters (emitted power, fluid velocity, concentration and properties of the suspension) is explored. The first part evaluates the ultrasonic wave attenuation caused by both the cavitation and the solid particles, as well as the characteristics of its frequency spectrum. Indeed, acoustic bubbles have their own acoustic signature. For this purpose, acoustic pressure measurements are carried out along the reactor with a piezoelectric hydrophone and the signals are interpreted by a spectral analysis. The second part quantifies the physical effects of ultrasounds via a local measurement of liquid-solid mass transfer coefficient by an electrochemical method. The axial mapping of the reactor using microelectrodes can identify the zones of strong intensification. Compared with the previous measurements, they also reveal the link between the local mass transfer enhancement and the characteristics of the acoustic signal measured nearby. Finally, the experimental study is completed by numerical simulations of the reactor carried out by COMSOL Multiphysics. The model includes the energy dissipated by the bubbles, which is a key factor of ultrasound attenuation. Via a parametric study, those simulations also show the role of the sono-reactor design on the localization of active zones

Acousto-electric (AE) effect comes from an interaction between electrical current and acoustic pressure generated when acoustic waves travel through a conducting material. It currently has two main application areas, ultrasound current source density imaging (UCSDI) and AE hydrophone. UCSDI can detect the current direction by modulating the dipole field with ultrasound pulse, and it is now used to form 3D imaging of dipole changing in one period of treatment, such as arrhythmia in the heart and epilepsy in the brain. As ultrasound pulse passes through electrical field, it convolutes or correlates with the inner product of the electric fields formed by the dipole and detector. The polarity of UCSDI is not determined by Doppler effect that exists in pulse echo (PE) signal, but the gradient of lead field potentials created by dipole and recording electrode, making the base-banded AE voltage positive at the anode and negative at cathode. As convolution shifts spectrum lower, the base band frequency for polarity is different from the center frequency of AE signal. The simulation uses the principles of UCSDI, and helps to understand the phenomena in the experiment. 3-D Fast Fourier Transform accelerates the computing velocity to resolve the correlation in the simulation of AE signal. Most single element hydrophones depend on a piezoelectric material that converts pressure changes to electricity. These devices, however, can be expensive, susceptible to damage at high pressure, and/or have limited bandwidth and sensitivity. An AE hydrophone requires only a conductive material and can be constructed out of common laboratory supplies to generate images of an ultrasound beam pattern consistent with more expensive hydrophones. Its sensitivity is controlled by the injected bias current, hydrophone shape, thickness and width of sensitivity zone. The design of this device needs to be the tradeoff of these parameters. Simulations were made to optimize the design with experimental validation using specifically fabricated devices composed of a resistive element of indium tin oxide (ITO).